<!DOCTYPE html>
<html>
 <head>
  <style>
   span { color: red }
   :default + span { color: green }
   span.reverse { color: green }
   :default + span.reverse { color: red }
   input { display: none }
  </style>
 </head>
 <body onload="var foo = document.getElementById('foo');
               var bar = document.createElement('input');
               bar.type = 'submit';
               foo.appendChild(bar)">
  <form id="foo">
    <input type="submit"><span>This should be green</span>
  </form>
 </body>
</html>
